In rubber and rubber compositions for use in pneumatic tires, it is common to utilize processing oils to soften and extend the rubber. Typically, aromatic processing oils having a certain content of polycyclic aromatic (PCA) compounds or polyaromatic hydrocarbons (PAH) have been used. Recently, regulatory concerns have necessitated the use of processing oils having a lower PCA content.
Certain types of rubber, or rubbery polymers, are difficult to oil extend due to degradation of the polymer chains. For example, silica or tin coupled styrene-butadiene rubbers are not typically extended with conventional highly aromatic DAE oils because the oil renders the polymer unstable and significant Mooney viscosity loss is seen.
Metal coupled styrene-butadiene polymers are especially useful in tire compounds. Coupled SBR may be synthesized at high molecular weights, offering the advantage of low hysteresis compounds. However, use of these rubbers has heretofore been limited due to the problems in extending the rubbers with conventional highly aromatic oils. It would, therefore, be advantageous to be able to oil extend these types of rubbers without experiencing the level of degradation seen with aromatic oils.